JP2001223369A - End face incident waveguide type semiconductor photodetector and light receiving module using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waveguide type photoreceptor which has an end face incident structure which is superior in matching properties with a waveguide type optical device, can obtain a high horizontal position shift tolerance width and a high light receiving sensitivity, and can reduce simultaneously an electrostatic capacity. SOLUTION: This end face incident waveguide type photodetector element has a semiconductor mesa part 12 projecting in a trapezoidal manner, comprising: a core layer structured by a light absorbing layer 13 for absorbing lights and a semiconductor layer which has a lower refraction coefficient than the light absorbing layer across the light absorbing layer on one face of a semiconductor substrate 11, and is the type that a part of a side face of a semiconductor mesa part is set as a light receiving end face. A width of the semiconductor mesa part 12 is decreased along a progress direction of incident lights from the light receiving end face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge-illuminated semiconductor light receiving element, an optical module, and an optical transmission device used in the field of optical communication and the like.

[0002]

2. Description of the Related Art In recent years, a subscriber optical transmission system has been developed in order to expand an information service to general households. From the viewpoint of installation in each home, the optical module used in the present system is required to be reduced in price. For this, a light emitting element and a light receiving element that can be integrated on the same substrate by a simple mounting method are essential. 2. Description of the Related Art An optical device typified by a semiconductor laser diode, an optical modulator, an optical switch, or the like has a waveguide structure and emits light in and out of a substrate in a parallel direction. On the other hand, a semiconductor light receiving element is generally a surface light receiving type that receives an optical signal from a direction perpendicular to the substrate surface. Since the surface light receiving type semiconductor light receiving element has a different optical signal input / output direction from other optical devices, it is difficult to integrate them on the same substrate.

In order to solve the above problem, development of an edge-illuminated type semiconductor light receiving element has been advanced. The challenge is to achieve both high optical coupling efficiency with signal light and low voltage operation. However, the IEICE Electronics Society Conference, C-
334, "InGaAlAs waveguide type PI for surface mounting
N-PD with High Efficiency and High Reliability ”, 1996, width 4
A waveguide type light receiving element having a light receiving portion of 0 μm and a length of 100 μm and having an external quantum efficiency of 0.92 A / W has been reported.

[0004]

FIG. 8 shows an example of the above prior art. In FIG. 8, the width of the light receiving unit mesa 82 is W,
Let L be the length. The capacitance C of the light receiving portion mesa is C = εS / d, where S is the light receiving portion mesa area, d is the depletion layer width during operation, and ε is the dielectric constant of the light absorbing layer. In the above prior art, W is constant with respect to the traveling direction of the incident light, and S = W
L and C = εWL / d. Therefore, when W and L are increased in order to increase the horizontal optical coupling tolerance width and the light receiving sensitivity, there is a problem that the capacitance C increases and high-speed operation becomes difficult.

An object of the present invention is to provide an edge-illuminated light-receiving element which can obtain a high horizontal optical coupling tolerance width and a high light-receiving sensitivity, and at the same time, reduce the capacitance. Still another object of the present invention is to provide a light emitting element module or a light receiving module using the same as a light receiving element.

[0006]

According to the present invention, in order to solve the above-mentioned problems, a light-absorbing layer for absorbing light and a refractive index higher than the light-absorbing layer with the light-absorbing layer interposed therebetween are provided on one surface of the semiconductor substrate. A light receiving element having a semiconductor mesa portion having a core layer composed of a low semiconductor layer, and having a part of the side surface of the semiconductor mesa portion as a light receiving end surface, wherein the width of the semiconductor mesa portion is Is reduced along the traveling direction of incident light from the light receiving end face.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

FIG. 1 shows a perspective view of an embodiment of the present invention using an InGaAlAs-based compound semiconductor. p-InP
On the substrate 11, p is applied by molecular beam epitaxy (MBE).
-InAlAs buffer layer 19 (0.7 μm thickness), p
-InAlGaAs lower second core layer 18 (2 μm in thickness,
Band gap wavelength 1.1 μm), undoped InAl
A GaAs light absorption layer 13 (thickness 2 μm, band gap wavelength 1.4 μm), an n-InAlGaAs upper second core layer 22 (thickness 2 μm, band gap wavelength 1.1 μm),
n-InAlAs upper cladding layer 21 (1 μm thickness),
n-InGaAs contact layer 20 (0.1 μm thickness)
Are sequentially grown, and a light-receiving portion mesa 12 and a stud portion mesa 15 are formed by chemical etching. After that, SiN
The crystal surface is passivated by the insulating film 14 to form an opening only above the light-receiving portion mesa 12. Next, Ti /
An n-type electrode 16 and a p-type electrode 17 made of Pt / Au are formed by vapor deposition. A light-receiving end face is formed by cleavage, an antireflection film is formed, and the light-receiving end face is divided into element units to obtain a waveguide type light-receiving element of the present invention. The width of the light receiving part mesa is W on the light receiving end face side.
a = 40 μm, Wb = 5 μm on the opposite side, and the length of the light receiving part mesa is L = 100 μm.

In an end-surface incident type waveguide light receiving device having a light receiving portion mesa 12 as shown in FIG.
2 is the maximum Wa at the light receiving end face, and decreases to Wb along the traveling direction of the incident light. Light receiving part mesa area S
= (Wa + Wb) L / 2, which is characterized in that it is smaller than the mesa area S = WL of the light receiving portion in the above-mentioned conventional technology.
For this reason, even when Wa is increased to increase the horizontal optical coupling tolerance width and L is increased to increase the light receiving sensitivity, the light receiving part mesa area S can be reduced, and the capacitance can be reduced. is there.

FIG. 2 shows the relationship between Wb and capacitance C when Wa = 40 μm and L = 100 μm. In the case of the conventional structure in which W is constant with respect to the traveling direction of the incident light and Wb = Wa = 40 μm, the capacitance becomes 0.3 pF or more. The capacity is reduced. By setting Wb = 5 μm, the capacitance can be reduced to 0.2 pF or less.

FIG. 7 is an explanatory diagram in the case where signal light from a single mode fiber is incident on the element of the present invention. The effect when the signal light having a wavelength of 1.3 μm from the single mode fiber 71 is incident will be described with reference to FIG. The divergence angle from the single mode fiber 71 (the light output intensity is 1 /
defined at an angle a e ²⁾ is θ ₀ = 5.6 °, after entering the light receiving mesa 12, the angle of incident on the mesa side surface is θe = 78.4 °. This is the critical angle θc for total reflection
_{^{= Sin -1 (n b / n}} e) = 37.3 for sufficiently larger than °, is totally reflected guided by the light receiving mesa 12. Where _{n b} is the refractive index of the SiN insulating film 14, _{n e} is an equivalent refractive index of the light receiving mesa 12. Note that a high-reflection film made of a dielectric multilayer film may be formed on the side surface of the semiconductor mesa. As a result, a high light receiving sensitivity as high as 0.92 A / W is obtained at a bias voltage of 1.2 V, and the tolerance for positional deviation with respect to the single mode fiber 71 is ± 0.5 dB in the vertical direction when degraded by 0.5 dB.
2.0 μm, ± 15.0 μm in the horizontal direction, enabling surface mounting using the passive alignment method (a method of obtaining optical coupling only by adjusting the mounting position of each component without monitoring the light receiving sensitivity) Become. Further, the light receiving part mesa area S
= (Wa + Wb) L / 2 = 2250 μm ² , the capacitance of the light receiving section can be reduced to 0.18 pF, and a cutoff frequency of 10 GHz or more can be obtained at a bias voltage of 1.2 V.

The same effect can be obtained even if the above-mentioned structure is constituted by an InGaAsP-based semiconductor layer.

The light absorbing layer 13 has a wavelength of 1.55 μm.
The same effect can be obtained by using a semiconductor layer having light receiving sensitivity for the signal light.

FIG. 3 shows a perspective structure of an application example using the waveguide type light receiving element of the present invention. The waveguide type light receiving element 31 of the present invention is optically mounted on an optical waveguide substrate 36 having a quartz optical circuit 35 such as an optical coupler or an optical multiplexer / demultiplexer in which an optical waveguide is embedded, an insulating film 34, and electric wirings 32 and 33. It is mounted using a passive alignment method without a lens. The n-type electrode of the waveguide type light receiving element 31 is connected to the electric wiring 32 by AuSn solder, and the p-type electrode is connected to the electric wiring 33 by Au wire bonding.

When the device is mounted, the displacement of the substrate in the horizontal direction is within ± 1 μm, and the coupling loss accompanying this is 0.2 d.
B or less. As a result, for a 1.3 μm signal light, 0.87 A /
High light receiving sensitivity of W or more can be obtained. Further, the capacitance of the light receiving unit can be reduced to 0.18 pF, and a cutoff frequency of 10 GHz or more can be obtained.

FIG. 4 shows a perspective structure of another application example using the waveguide type light receiving element of the present invention. Insulating film 34, electric wiring 3
The waveguide type light receiving element 31 of the present invention is flip-chip mounted on the V-groove substrate 41 having the elements 2 and 33 by using a passive alignment method without an optical lens. The n-type electrode of the waveguide type light receiving element 31 is an electric wiring 3 made of AuSn solder.
2 and the p-type electrode is connected to the electric wiring 33 by Au wire bonding. After that, the flat end optical fiber 42 is fixed to the V groove.

The positional deviation when mounting the element and fixing the optical fiber is within ± 1 μm, and the coupling loss accompanying this is 0.2 μm.
It can be reduced to dB or less. As a result, for a 1.3 μm signal light, 0.87 A at a bias voltage of 1.2 V.
/ W or higher light receiving sensitivity is obtained. Furthermore, the capacitance of the light receiving section can be reduced to 0.18 pF, and the
The above cutoff frequency is obtained.

FIG. 5 shows a waveguide type light receiving element of the present invention.
1 shows a perspective structure of one embodiment of a packaged light receiving element module. A waveguide type light receiving element 55 of the present invention, a receiving preamplifier (preamplifier) IC 56 on a V-groove substrate 54
Is surface mounted. Here, the passive alignment method can be used for mounting the waveguide type light receiving element 55.
After that, the optical fiber 52 for signal light incidence is fixed in the V-groove. The V-groove substrate 54 is fixed to a ceramic base 53, and hermetically sealed by laser welding or the like with a metal cap 51 and packaged.

[0019] The same applies even when a transfer mold is made of resin instead of the base and the cap.

The produced optical module was evaluated for transmission. In burst transmission with a signal light wavelength of 1.3 μm and a transmission speed of 50 Mbit / s, an error rate of 10 −8 and −38 d
A minimum receiving sensitivity of Bm was obtained.

In place of the ceramic base 53, resin or metal may be used. The same applies to the case where a resin transfer mold is used instead of the ceramic base 53 and the metal cap 51. Further V
The same applies to the case where an optical waveguide substrate having an optical circuit is used instead of the groove substrate 54.

FIG. 6 is a bird's-eye view of one embodiment of an optical receiving module using the waveguide type light receiving element of the present invention. A light receiving element module 64 equipped with the waveguide type light receiving element of the present invention and having an optical fiber 63 for signal light incidence and a receiving IC 61
And other electronic components are mounted on the board 62. The receiving IC 61 constituting the receiving circuit includes a main amplifier circuit which receives and amplifies an output of a preamplifier (preamplifier) as an input, and a timing extracting circuit which receives the output of the main amplifier circuit as an input, extracts timing, and outputs a clock. An identification reproduction circuit that receives and outputs a main amplifier output and a clock and performs identification reproduction;
It is composed of an alarm circuit when there is no signal, an entire power supply circuit and the like. This optical receiving module was evaluated for transmission. In burst transmission with a signal light wavelength of 1.3 μm and a transmission speed of 50 Mbit / s, a minimum receiving sensitivity of −38 dBm or less was obtained at an error rate of 10 ⁻⁸ , and it was possible to meet the requirements of long-distance transmission systems. In addition, by using a 10 Gbit / s transmission circuit for a receiving IC, etc., the transmission speed is 10 Gbit / s.
/ S, an error rate of 10 ⁻¹² , a minimum receiving sensitivity of −16 dBm or less was obtained, and high-bandwidth transmission could be supported.

[0023]

By using the waveguide type light receiving element of the present invention,
With the low-voltage operation, high light-receiving sensitivity can be obtained, the horizontal positional deviation tolerance width for the signal light can be increased, and the capacitance of the light-receiving unit can be reduced. As a result, a large mounting margin can be obtained, optical coupling can be easily obtained without an optical lens, and high-band receiving characteristics can be obtained. Therefore, it is possible to manufacture a light receiving element, a light receiving element module, an optical receiving module, and an optical transmission device with low cost and high transmission speed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a structure of an edge-incident waveguide type light receiving element of the present invention.

FIG. 2 shows a correlation between the length L of the light receiving part mesa 12 and the mesa area S of the light receiving part.

FIG. 3 shows a perspective structure of an application example of the edge-incident waveguide type light receiving element of the present invention.

FIG. 4 shows a perspective structure of another application example of the end face incidence waveguide type light receiving element of the present invention.

FIG. 5 shows a perspective structure of a light receiving element module of the present invention.

FIG. 6 shows a bird's-eye view of the entire structure of the receiving module of the present invention.

FIG. 7 shows that light incident on the light receiving element of the present invention is totally reflected.

FIG. 8 shows a perspective structure of a conventional edge-incident waveguide type light receiving element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... p-InP substrate, 12 ... light receiving part mesa, 13 ... undoped InAlGaAs light absorption layer, 14 ... SiN insulating film, 15 ... stud part mesa, 16 ... n-type electrode, 17 ... p-type electrode, 18 ... p-InAlGaAs Lower second core layer, 19 p-InAlAs buffer layer, 20 n-InGaAs contact layer, 21 n-InAlAs upper cladding layer, 22 n-InAlGaAs upper second core layer, 31 waveguide type of the present invention Light receiving element, 32: electric wiring, 33: electric wiring, 34: insulating film, 35: quartz optical circuit, 36: optical waveguide substrate, 41: V-groove substrate, 42: optical fiber, 51: cap, 52: optical fiber Reference numeral 53: base, 54: V-groove substrate, 55: waveguide type light receiving element, 56: reception preamplifier (preamplifier) IC, 61: reception IC, 6 ... Board, 63 ... Optical fiber, 64 ... Light receiving element module, 71 ... Single mode fiber, 81 ... P-InP substrate, 82 ... Light receiving part mesa, 83 ... Undoped InAlGaAs light absorbing layer, 84 ... SiN insulating film, 85 ... Stud mesa, 86 ... n-type electrode, 87 ... p-type electrode.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masato Shishikura 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 2H037 AA01 BA11 CA39 DA03 DA04 DA12 5F073 AB18 AB28 BA01 FA07 FA16 5F088 AA03 AB07 BA01 BA02 BA16 BB01 DA17 EA07 EA09 FA09 GA03 GA07 GA10 JA20 KA02 KA08 KA10

Claims (5)

[Claims] 1. A semiconductor substrate comprising, on one surface of a semiconductor substrate, a light absorbing layer for absorbing light and a core layer sandwiching the light absorbing layer and comprising a semiconductor layer having a lower refractive index than the light absorbing layer. An end face incident waveguide type light receiving element having a semiconductor mesa portion protruding in a trapezoid shape and having a part of the side surface of the semiconductor mesa portion as a light receiving end surface, wherein the width of the semiconductor mesa portion is incident light from the light receiving end surface. Characterized in that it decreases along the direction of travel of the end facet waveguide type semiconductor light receiving element. 2. The end face incident waveguide type semiconductor light receiving element according to claim 1, wherein incident light incident from said light receiving end face is totally reflected by a side face of said semiconductor mesa portion. A second semiconductor mesa portion having substantially the same height as the semiconductor mesa portion on one surface of the semiconductor substrate; and an n-type electrode provided on the semiconductor mesa portion and the second semiconductor mesa portion. 3. The end face incident waveguide type semiconductor light receiving device according to claim 1, wherein a p-type electrode is provided on the other surface of the semiconductor substrate. 4. An optical fiber for transmitting a signal light, a V-groove substrate having a V-groove for holding the optical fiber, optically coupled to the optical fiber, photoelectrically converting the signal light and outputting an electric signal. 4. An optical fiber comprising: an end facet waveguide type semiconductor light receiving element according to claim 1; a preamplifier for amplifying the electric signal; and a terminal for transmitting an output of the preamplifier; And a V-groove substrate, the light-receiving element, and the preamplifier are hermetically sealed and integrated with a base and a cap. 5. A light-receiving element module according to claim 4, a main amplifier for amplifying the output of the preamplifier of the light-receiving element module, and a timing extraction for receiving the main amplifier output as an input, extracting a timing, and outputting a clock. A receiving circuit composed of a main amplifier output and the clock, and an identification regenerator that performs identification and reproduction by using the clock as input and outputs signal data; and a printed wiring board on which the light receiving element module and the receiving circuit are mounted. An optical receiving module characterized by the above-mentioned.